1. Field of the Invention
This invention is generally related to traffic management in a downstream line card.
2. Background Art
In a Data Over Cable Service Interface Specification (DOCSIS) system, a Cable Modem Termination System (CMTS) transmits downstream network traffic to a cable modem using the DOCSIS protocol over one or more Quadrature Amplitude Modulated (QAM) channels. In the simplest case, downstream data is transmitted over a single channel to the cable modem thereby limiting the bandwidth to the maximum rate supported by the single channel. The downstream bandwidth can be increased by using multiple channels for a data flow which is referred to as “channel bonding.” A set of channels used for channel bonding may be referred to as a “bonded channel group.” The maximum possible rate for a bonded channel group is the sum of the maximum rates of the channels that comprise the group. Furthermore multiple bonded channel groups can exist in a single DOCSIS system.
Channel bonding adds complexity to the scheduling of downstream network traffic entering a CMTS. In systems without channel bonding, each data flow is associated with a single channel. Each channel can have multiple data flows associated with it. The traffic from the associated data flows is simply shaped to the maximum rate supported by the channel. However, with the introduction of channel bonding, a data flow is either associated with a single channel or to one of the bonding channel groups. Since each channel may correspond to one or more bonded channel groups as well as being a standalone channel, simply rate-shaping each channel and bonded channel group to its maximum possible rate may result in an oversubscription scenario where packets are dropped.
Methods, systems and computer program products are needed to overcome the above mentioned deficiencies.
The present invention will now be described with reference to the accompanying drawings. In the drawings, like reference numbers may indicate identical or functionally similar elements. Additionally, the left-most digit(s) of a reference number may identify the drawing in which the reference number first appears.